I don't know enough about chemistry to explain the differences between acetal and, say, polystyrene. Acetal machines well, and has great tolerance.
I don't have any reason for wanting to use it other than the fact that I have access to it, and the capability to mill it. I could make one of the metal units like you posted as well.
Acetal is just a carboxylic acid group name for anything that has a CH3C=O
The name of the plastic is polyacetal or polyoxymethylene (POM), or the Dupont trademark name of Delrin.
polymer means that there are many of the mer single units. In the case of delrin it is multiple units of acetal or the CH3CO linked to more of the same like this:
Delrin is great when machined because the base stock is free from bubbles that form when it is heated for extrusion. It is not impervious, don't spill clorox bleach on it because the chlorine will attack the polymer and degrade it. It has also been found to degrade in UV radiation and have a high degree of thermal expansion, like most polymers.
polystyrene has the styrene mer which is an arene meaning it has a benzene ring (hexagon of carbon atoms).
As for the hopup nub... anyone remember the H-hop craze?
